Different surgeries are used to treat stage III Adult Acquired Flatfoot Deformity. Some include hindfoot manipulation with subtalar fusion (single fusion), triple fusion (subtalar, talonavicular, and calcanealcuboid), and triple fusion with additional midfoot and forefoot manipulation. This study aimed to compare the effect of these surgeries on the unloaded and loaded foot, using a validated dynamic computational model. Five patients with stage III flatfoot underwent pre-surgical and post-surgical CT scans. Dynamic computational models were created for four groups:​ pre-operative, single fusion, triple fusion, and triple fusion with additional maneuver. A control group was based on models from nine cadaveric normal feet. Once the effect of the surgeries on foot architecture was assessed, the response of the foot to bodyweight was evaluated. All surgeries changed the unloaded foot architecture towards normal. Triple fusion following the additional manipulation produced the best correction, but reduced talonavicular coverage. Under bodyweight, it was observed that, for the triple fusion surgeries, particularly after additional manipulation, foot rigidity and contact forces under the fourth and fifth metatarsal bones increased. Moreover, all surgeries moved the tibiotalar contact position to an area previously reported to have a lower risk of osteoarthritis. Clinical significance:​ the study results suggest that single fusion surgery corrects the deformity, with less risk of overcorrection, compared to the other techniques. However, triple fusion is necessary when osteoarthritis affects the Chopart joint.